54 RECONNAISSANCE Hi NORTHERN ALASKA IN 1901. 



which may possibly be veins), one dark and the other light. These supposed dikes 

 are thin, and they are younger than the schistosity of the country rock. The dark 

 ones are the older, and cut the lock for the most part obliquely to the schistosity or 

 bedding, which they slightly exceed in dip. the dip being to the north, at an angle of 

 about 45 ; . The light dikes cut the rocks at nearly right angles to the dark dikes 

 and dip south at an angle of about 80°, and seem to follow fault planes or fissures 

 that were manifestly produced subsequent to the intrusion of the dark dikes. 



The above division of the rocks is based largely on paleontologic evidence. But 

 the Totsen series, in which no fossils were found, is assigned to a low place in the 

 geologic scale by reason of its ciystalliue character or high degree of metamorphism 

 and the known relatively low stratigraphic position in which similar rocks occur in 

 adjacent regions. The Stuver series, in which likewise no fossils were found, is 

 regarded as among the older rocks by reason of its field relations to the overlying 

 Devonian. 



After the deposition of the oldest Paleozoic sediments occurring in the present 

 southern axis of the main range, this part of the region seems to have been uplifted 

 and subjected to dynamic action and metamorphism, following which a portion of 

 the field probabky remained above sea during the whole or a part of the period 

 in which the Devonian sediments were being laid down in the region now occupied 

 by the northern axis. During this period of deposition, which possibly extended 

 into earty Mesozoic, the later Paleozoic sediments, including apjiarently the Car- 

 boniferous, seem to have been deposited unconformable against the older rocks 

 of the southern axis. This period was followed by stress, uplift, and the exertion 

 of mountain-building forces, resulting in folding, metamorphism, and deformation 

 of the strata. 



Then followed a long pause, during which the reduction of the land area by 

 subaerial erosion nearly to sea level gave rise to the peneplain or formerly nearly 

 level surface of the Endicott Plateau. This base-level ing~was, in turn, followed by 

 elevation of the region, whence upward movement seems to have continued more or 

 less intermittently down to the present time. Uplift was accompanied by vigorous 

 dissection of the plateau, from which the Endicott Mountains, as we find them 

 to-day, seem manifestly to have been carved. 



Contemporaneous with this uplift and dissection the sediments eroded from the 

 range were borne to the sea and deposited as new terranes on both the north and 

 the south side of the mountains. These later deposits range in age from Middle 

 Mesozoic to recent. Though throughout this period the Endicott Plateau seems to 

 have stood above the sea, the i - egion was subjected to somewhat pronounced changes 

 of level and disturbance, as is evidenced by deformation and unconformities extend- 

 ing- from Middle Mesozoic to Pleistocene. 



